Toluene and styrene intoxication route in the rat cochlea.

It is well established that organic solvents such as toluene and styrene are ototoxic in the rat; however, the intoxication route used to reach the organ of Corti is still questionable. The distribution of toluene and styrene in various tissues of Long-Evans rats (n = 2 x 8) was studied after inhalation of either 1750 ppm toluene or 1750 ppm styrene for 10 h (6 consecutive h + 4 h the following day). At the end of the solvent exposures, blood, brain, auditory nerves, the organ of Corti, cerebrospinal (CSF), and inner ear fluids (IEF) were sampled or removed to measure the rates of solvent uptake in each tissue by gas chromatography. Results indicate that CSF and IEF were free from detectable solvents, whereas the organ of Corti, the nerves, and the brain were contaminated. Therefore, both toluene- and styrene-induced hearing losses are caused by tissue intoxication rather than by fluid contamination. It is proposed that the outer sulcus is used as an intoxication route to reach the organ of Corti.